In recent years, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries and nickel hydrogen batteries have been widely used as so-called portable power sources for personal computers, hand-held terminals, and the like, and as power supplies for vehicle propulsion. In particular, light weight lithium ion secondary batteries able to achieve high energy densities can be advantageously used as high output power sources for propelling vehicles such as electric vehicles and hybrid vehicles.
In such non-aqueous electrolyte secondary batteries, a part of the non-aqueous electrolyte (for example, a non-aqueous solvent or supporting electrolyte) decomposes during initial charging, and a coating film comprising a decomposition product thereof (for example, an organic layer of ROCO2Li or the like, or an inorganic layer of LiF, Li2O, or the like) is formed on the surface of the negative electrode active material. This coating film can suppress reductive decomposition of the non-aqueous electrolyte during subsequent charging and discharging, and can improve the durability (for example, the cycle characteristics) of the battery. As a related feature, Patent Literature 1 discloses a lithium ion secondary battery in which a non-aqueous electrolyte contains an oxalate complex compound (for example, lithium bis(oxalato)borate).